How do IT companies find their customers?

We are a young mobile product agency (launched the business just a few months ago) that speci
alizes in designing and developing applications for iOS and Android. Currently working on a few small projects we managed to get by bidding for them on different bidding platforms.

As a new business, we find it pretty challenging to find clients.
We obviously don’t have a portfolio that speaks for itself yet, neither do we have a good reputation to help us out.
Therefore, we would really appreciate if some experienced business owners could share some of their approaches, tips and tricks.
How do companies like ours find and attract new customers inside and outside the US?
Thank you all very much in advance!